C++知識點(8）_istringstream的用法

isstringstream對象可以綁定一行字符串，然後以空格爲分隔符把該行分割開。
添加頭文件:#include
工程實例：
比如讀取文件：data.txt
L 0 0 1477010443349642 0 0 0 0
R 0 0 0 1477010443349642 0 0 0 0
工程實現：
頭文件定義數據類型：

class MeasurementPackage {
public:
  long long timestamp_;

  enum SensorType{
    LASER,
    RADAR
  } sensor_type_;

  Eigen::VectorXd raw_measurements_;
};

class GroundTruthPackage {
public:
  long timestamp_;

  enum SensorType{
    LASER,
    RADAR
  } sensor_type_;

  Eigen::VectorXd gt_values_;

};

    std::string input_file_name = "..data.txt";
    // 打開數據，若失敗則輸出失敗信息，返回-1，並終止程序
    // Open file. if failed return -1 & end program
    std::ifstream input_file(input_file_name.c_str(), std::ifstream::in);
    if (!input_file.is_open()) {
        std::cout << "Failed to open file named : " << input_file_name << std::endl;
        return -1;
    }
    std::vector<MeasurementPackage> measurement_pack_list;
    std::vector<GroundTruthPackage> groundtruth_pack_list;
    std::string line;
    while (getline(input_file, line)) 
    {
        std::string sensor_type;
        MeasurementPackage meas_package;
        GroundTruthPackage gt_package;
        std::istringstream iss(line);
        long long timestamp;

        // 讀取當前行的第一個元素，L代表Lidar數據，R代表Radar數據
        // Reads first element from the current line. L stands for Lidar. R stands for Radar.
        iss >> sensor_type;
        if (sensor_type.compare("L") == 0) {
            // 激光雷達數據 Lidar data
            // 該行第二個元素爲測量值x，第三個元素爲測量值y，第四個元素爲時間戳(納秒）
            // 2nd element is x; 3rd element is y; 4th element is timestamp(nano second)
            meas_package.sensor_type_ = MeasurementPackage::LASER;
            meas_package.raw_measurements_ = Eigen::VectorXd(2);
            float x;
            float y;
            iss >> x;
            iss >> y;
            meas_package.raw_measurements_ << x, y;
            iss >> timestamp;
            meas_package.timestamp_ = timestamp;
            measurement_pack_list.push_back(meas_package);
        } else if (sensor_type.compare("R") == 0) {
            // 毫米波雷達數據 Radar data
            // 該行第二個元素爲距離pho，第三個元素爲角度phi，第四個元素爲徑向速度pho_dot，第五個元素爲時間戳(納秒）
            // 2nd element is pho; 3rd element is phi; 4th element is pho_dot; 5th element is timestamp(nano second)
            meas_package.sensor_type_ = MeasurementPackage::RADAR;
            meas_package.raw_measurements_ = Eigen::VectorXd(3);
            float rho;
            float phi;
            float rho_dot;
            iss >> rho;
            iss >> phi;
            iss >> rho_dot;
            meas_package.raw_measurements_ << rho, phi, rho_dot;
            iss >> timestamp;
            meas_package.timestamp_ = timestamp;
            measurement_pack_list.push_back(meas_package);
        }

        // 當前行的最後四個元素分別是x方向上的距離真值，y方向上的距離真值，x方向上的速度真值，y方向上的速度真值
        // read ground truth data to compare later
        float x_gt;
        float y_gt;
        float vx_gt;
        float vy_gt;
        iss >> x_gt;
        iss >> y_gt;
        iss >> vx_gt;
        iss >> vy_gt;
        gt_package.gt_values_ = Eigen::VectorXd(4);
        gt_package.gt_values_ << x_gt, y_gt, vx_gt, vy_gt;
        groundtruth_pack_list.push_back(gt_package);
    }